Combination weighing apparatuses used for automated weighing of a variety of articles are provided with multiple weighing hoppers. With this kind of combination weighing apparatus, articles are dispersed/supplied to each of the weighing hoppers through pool hoppers correspondingly arranged above the weighing hoppers. Next, the weights of the articles in the weighing hoppers are measured and a combinational computation is performed based on the measured weight values. Then, the optimum combination for which the combined weight is within a prescribed allowed error tolerance and closest to a target weight is calculated and only the articles in the weighing hoppers corresponding to this optimum combination are discharged. As a result, the combination weighing apparatus obtains the article with the weight that is closest to the target weight.
In some cases, the hoppers are so constructed as to include a pipe-like body (box-like body) that is open at the top and bottom, a gate that is attached in a freely swingable manner to the pipe-like body and serves to open and close the bottom opening of the pipe-like body, and a link mechanism serving to transfer a driving force from an external drive source in such a manner as to swing the gate. In this type of hoppers, the link mechanism is formed complexly with the nuts, bolts, link members, and other parts, so debris and dust readily accumulates on the component members and connection portions of the link mechanism. Therefore the component members and connection portions of the link mechanism are sometimes covered with a cover.
An example of attaching a cover to a combination weighing apparatus is the invention disclosed in Japanese Laid-Open Patent Publication No. 2001-264153. The apparatus disclosed in that publication is provided with a hollow hopper support arm. The hollow hopper support arm extends from the main unit to the hopper and encloses a power transmission mechanism configured to transmit power from the drive source to the link mechanism. Thus, since the power transmission mechanism and the link mechanism are not exposed, accumulation of debris and dust on these mechanisms is avoided and the mechanisms are kept cleaner.
In another apparatus presented in Japanese Laid-Open Patent Publication No. 2001-349769, a lateral face of the main unit and the arm extending from the lateral face of the main unit are connected by a cover. Thus, the gap between the arm and an opening formed in the lateral face of the main unit is blocked and dust and moisture are prevented from entering the main unit.
In still another apparatus presented in Japanese Laid-Open Patent Publication No. 2001-349768, a plurality of covers are provided—one for each vertical column of hoppers arranged around the outside of the main unit. The covers are made of stainless steel or other metal that has been shaped by bending and are attached to each vertical column of hoppers such that the upper surface of each cover covers approximately the rear half of a conveying trough, where “rear” is defined in terms of the conveying direction. The front and lateral faces of the covers cover the top inlet openings and the entire lateral face of the stock hoppers and weighing hoppers as well as the top inlet openings and the approximately the upper half of the lateral faces of the memory hoppers. As a result, debris and other contaminants can be prevented from entering through the inlet openings of the hoppers.
However, although the apparatuses presented in Japanese Laid-Open Patent Publication No. 2001-349768 and Japanese Laid-Open Patent Publication No. 2001-349769 are configured to prevent the accumulation of debris and dust and the like inside the main unit and the link mechanism, these apparatuses are not able to solve the following problem. Namely, fragments of resin parts and other component parts that have been damaged by the vibrations resulting from opening and closing the gate can fall and become mixed into the articles, and bolts, nuts, and other parts of the link mechanism that have become loose due to vibrations can also fall and become mixed into the articles. This problem is particularly apparent when the gate is opened and closed at a high speed in order to improve productivity.
Additionally, while it can prevent fragments, bolts, and nuts from becoming mixed with the articles, the apparatus presented in Japanese Laid-Open Patent Publication No. 2001-264153 is configured such that the portion from the power transmission mechanism to the link mechanism is enclosed inside a hollow hopper support arm. Consequently, bolts, nuts, and other items that have fallen cannot easily be removed. Furthermore, the cover structure is complex and disadvantageous in terms of manufacturing ease and cost.